A proffer can have different meanings depending on the context in which it is used. Here are some of the most common definitions:

• In a trial, to proffer is to offer evidence in support of an argument, or elements of an affirmative defense or offense. A party with the burden of proof must proffer sufficient evidence to carry that burden.

• In pretrial negotiations, a proffer refers to an informal offer of information by an individual, usually a target, but sometimes a witness or subject, to one or more law enforcement officials. Most commonly, proffers are a prelude to cooperation. The individual is under investigation or has been charged with a crime and wants to offer information to law enforcement authorities in exchange for some benefit, such as dropped or reduced charges or an agreement for a lower sentence.

• A proffer session is the most common way to cooperate with the government in a criminal case. In exchange, the defendant gets use immunity. During a proffer session, the defendant is represented by counsel and the government is represented by the federal prosecutor along with the investigating agents. The defendant is expected to share with the government everything they know about the crime in question and the people involved. The defendant is legally required to tell the truth and not withhold any relevant information. The government may use the proffer information at trial if the defendant has broken the agreement.

The word "proffer" is derived from Anglo-French "por-", forth, and "offrir", to offer.